The following files below are for the chat box. Notice how each appears to have a compass position. Well that’s what it is. Get used to it you will see it a lot.
box_chat_e.tga, box_chat_n.tga, box_chat_ne.tga
box_chat_nw.tga, box_chat_s.tga ,box_chat_se.tga
box_chat_sw.tga, box_chat_w.tga

Courtesy of Zonochio of the DDO Forums (Reposted)
Here are a few more:
tab_front_e
tab_front_n
tab_front_w
---->Selected tab (Stats in the picture)
tab_bg_e
tab_bg_n
tab_bg_w
---->Bar just below the tabs
tab_back_highlight_e
tab_back_highlight_n
tab_back_highlight_w
----> When you move the mouse over a tab (Skills in the picture)
tab_back_e
tab_back_n
tab_back_w
---->Other tabs on the page

headerTab* Headers for sorting the lists on the Social Panel tabs
sort_arrow_* Arrows for sort order on the Social Panel lists

left
topLeft
top
topRight
right
bottomRight
bottom
bottomLeft
---->Border on Filter + Comment sections of Who Tab and Add section of Friends Tab
box_ebdark_* is used for the Stat tab and Adventure Compendium as well as chat